Unidimensionality: The Original Sin of Educational Measurement

• In Event: Innovative Cognitive Approaches to Learning and Assessment

Abstract

Unidimensionality is perhaps the most foundational assumption of the dominant psychometric approach in large scale educational assessment in the United States. Unfortunately, the assumption and requirement of unidimensionality is at odds with the domain models on which those assessments are supposed to report. Therefore, unidimensionality serves to weaken—or even entirely obscure—the interpretability of test scores for their desired and/or intended purposes. This paper explores this tension, explains how the assumption and requirement of unidimensionality leads directly to weaker alignment with domain models, harms fidelity to blueprint through the test development process and thereby is particularly responsible for the ever worsening reputation of large scale assessment because of the harm it does to test validity.

Author

• Alexander M. Hoffman, AleDev Research